Add component to Custom Control's child component

I have created a custom control which is a Titled Etched Border Container, i have successfully created the control and added it into scene builder.

But when i try to add components into the custom control, the components are adding into the parent container of the custom control which is "AnchorPane" in this case, where as i want to add it into the child container "Pane" of the custom control.

It's just a mather of draging it in the right position...
I kind of think it's a weird question... why don't you just change it in you fxml file yourself instead of trying to achieve it with scenebuilder?

OP: I'm pretty sure that what you want to do is impossible. If I just look at HFXGroupPane.fxml, what I see is a custom AnchorPane with a StackPane inside. I don't see any reason that added controls would go in the StackPane unless you added them to the Stack Pane.